Mental Maths Lesson 1

Divisible rules.

If a number is divisible or not means if it is divisible no remainder left.

divisible by 2 --> When last number is even number or ends with 0, then it is divisible by 2.

Eg) 1234 , 1569850 , 6548 or 8989012

divisible by 3 --> When adding all digit numbers and if that number is divisible by 3 then original number is divisible by 3.

Eg) 12342 (sum of all digits is 12, 12 is divisible by 3 therefore 12342 is divisible by 3)

15698502(sum of all digits is 36, 36 is divisible by 3 therefore 15698502 is divisible by 3)

6548(sum of all digits is 23, 23 is NOT divisible by 3 therefore 6548 is NOT divisible by 3)

Divisible by 4 --> 4 * 25 = 100, therefore any multiples of 100 is divisible by 4. Therefore we need to look at last 2 digits and if that number is divisible by 4 then original number is divisible by 4.

Eg) 1234580 (this number is 1234500 + 80, since 1234500 is multiple of 100, we just need to see if 80 is divisible by 4 or not, and 80 is divisible by 4 therefore 1234580 is divisible by 4)

7499912 (this number is 7499900 + 12, since 7499900 is multiple of 100, we just need to see if 12 is divisible by 4 or not, and 12 is divisible by 4 therefore 7499912 is divisible by 4)

Divisible by 5 --> see if the number ends with 0 or 5.

Eg) 12580 Yes, divisible by 5

129436 No, not divisible by 5.

158915 Yes, divisible by 5

That's it for lesson 1. I will come back with Lesson 2 soon.